1. Field of the Invention
The present invention relates to a lamp ballast circuit and a driving method thereof.
2. Description of the Related Art
Lamp ballast circuits control the driving of fluorescent lamps. In general, a fluorescent lamp has low power consumption. Further, the space in which a lamp ballast circuit is often positioned can be small, and hence the lamp ballast circuits themselves are often manufactured with a small size. Because of the size limit, the lamp ballast circuit typically does not contain a power factor correction circuit. Accordingly, the typical lamp ballast circuit has a very low power factor, and the total harmonic distortion (THD) of the input current is typically very high. Hence, it is difficult for the general lamp ballast circuit to satisfy the relevant IEC61000-3-2 standard for the THD thresholds of the current for lighting devices disclosed in Section 2, Part 3 of EMC for electromagnetic waves.
Further, when the THD of the input current is high, the current flows to a neutral line provided in the transmission cable, additional power loss or fire may occur, and hence additional measures are required.
Another problem arises from the fact that the typical lamp ballast circuit is not driven in a stable manner when the input voltage is unstable. In particular, when the input voltage is less than a rated voltage, power consumption of switches included in the lamp ballast circuit increase and the lamp ballast circuit may be damaged.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.